Tires are increasingly expected to provide higher and higher levels of performance characteristics. For instance, it is normally expected for tires to exhibit good traction characteristics on both dry and wet surfaces as well as low rolling resistance for good vehicle fuel economy. However, it has traditionally been very difficult to improve the traction characteristics of a tire without compromising its rolling resistance and treadwear. Low rolling resistance is important because good fuel economy is virtually always an important consideration. Reducing the weight of tires is also a goal of automobile and truck manufacturers because reduced weight results in improved fuel economy. Reducing the weight of tires is of particular importance in the case of aircraft tires. Good treadwear is also an important consideration because it is generally the most important factor in determining the life of the tire.
The traction, treadwear and rolling resistance of a tire is dependent to a large extent on the dynamic viscoelastic properties of the elastomers utilized in making the tire tread. In order to reduce the rolling resistance of a tire, rubbers having a high rebound have traditionally been utilized in making the tire's tread. On the other hand, in order to increase the wet skid resistance of a tire, rubbers that undergo a large energy loss have generally been utilized in the tire tread. In order to balance these two viscoelastically inconsistent properties, mixtures of various types of synthetic and natural rubber are normally utilized in tire treads. For instance, various mixtures of styrene-butadiene rubber and polybutadiene rubber are commonly used as a rubber material for automobile tire treads. However, such blends are not totally satisfactory for all purposes.
Rubbers having intermediate glass transition temperatures (−70° C. to −40° C.) compromise rolling resistance and treadwear without significantly increasing traction characteristics. For this reason, blends of rubbers having low glass transition temperatures and rubbers having high glass transition temperatures are frequently utilized to attain improved traction characteristics without significantly compromising rolling resistance or treadwear. However, such blends of rubbers having low glass transition temperatures and rubbers having high glass transition temperatures exhibit poor processability. This major disadvantage associated with such blends has greatly hampered their utilization in making tire tread compounds.
U.S. Pat. No. 2,885,381 discloses a composition of matter comprising a copolymer of a conjugated diene and a heterocyclic nitrogen containing monomer having a sole CH2═CH— substituent, such as 2-vinylpyridine, said copolymer having been compounded with 25–100 weight parts per 100 parts of said copolymer of a finely ground mineral pigment selected from the group consisting of silica and aluminum silicate as the sole reinforcing agent.
In recent years, there has been a trend to include silica as a filler in tire tread compounds to further improve traction characteristics. U.S. Pat. No. 5,036,133 discloses a vulcanizable rubber composition that is comprised of: (A) an uncured natural or synthetic isoprene rubber, or one or more uncured butadiene-based synthetic rubbers, or uncured blends thereof, said uncured rubbers being sulfur vulcanizable, (B) a silica filler, (C) sulfur, (D) an organic accelerator and (E) a vinylpyridine-butadiene interpolymer co-activator, said interpolymer co-activator (E) containing from about 20 percent to about 65 percent by weight of vinylpyridine units, the amount of said vinylpyridine-butadiene copolymer co-activator being from about 0.5 to 2 parts by weight per 100 parts by weight of said rubber.
Authors Wang et. al in the Journal of Applied Polymer Science, Vol. 78, 1879–1883 (2000) describe a process of making clay-rubber mixtures by mixing an SBR latex or a styrene-vinylpyridine-butadiene latex with the hydrophilic unmodified clay without quaternary ammonium salts. In the case of the styrene-vinylpyridene-butadiene latex and clay composite, the expansion of clay gallery in the case of styrene-vinylpyridine composite was reported to increase from 1.24 to 1.46 nm, which is not significant enough. The intercalation of the rubber was minimal and very limited exfoliation is evident from stacks of clay layers as shown in the TEM micrographs for the said composite. The limited extent of intercalation is not expected to provide substantial property enhancement in tire materials. The article does not suggest of achieving a light-weight rubber composition and a tire with improved rolling resistance. The intercalation achieved by using the organically modified clay with quaternary ammonium surfactant by mixing it in a solution of rubber is also described, that resulted in somewhat better intercalation or expansion of clay galleries. Nevertheless, the mixing time of 12 hours was used, which is rather long for an industrial process. The publication does not disclose a bulk thermomechanical mixing method of making rubber-clay nanocomposite with uniform dispersion and high degree of exfoliation that will result in a light weight composition and lower hysteresis.
European Patent Application EP1029823 A2 describes preparation of rubber composite materials. This European Patent Application discloses a composite clay rubber material comprising at least one material selected from the group consisting of a first composite clay material and a second composite clay material; and a rubber material; said first composite material comprising a clay mineral having interlayer section; an onium ion having 6 or more carbon atoms, bonding to said clay mineral via an ionic bond for expanding said interlayer section and rendering said interlayer section compatible with an organic molecule; a first guest molecule having a polar group therein being at least partially incorporated into said expanded interlayer section and bonded to said clay mineral through a hydrogen bonding between said clay mineral and said polar group; and a second guest molecule as said organic molecule without a polar group as said organic molecule being at least partially incorporated into said expanded interlayer section, said first guest molecule having a molecular length equal to or smaller than that of said onium ion, said second guest molecule having a molecular length equal to or larger than that of the said onium ion; said second composite clay material comprising a clay mineral having an interlayer section; an onium ion having 6 or more carbon atoms, bonding to said clay mineral via ionic bond for expanding said interlayer section and rendering said interlayer section compatible with an organic molecule; and a main guest molecule as said organic molecule having a polar group in a main chain and/or side chain thereof being at least partially incorporated into said expanded interlayer section and bonded to said clay mineral through a hydrogen bonding between said clay mineral and said polar group, said main guest molecule having a molecular length equal to or larger than that of the said organic onium ion-wherein said organic onium ion contained in at least one of said first composite clay material and said second composite clay material is crosslinked with at least one of said second guest molecule and said main guest molecule and a molecule of said rubber material.
European Patent 1029823 A2 further describes that crosslinking be provided by using the onium ions with unsaturated groups for crosslinking with the guest molecule and rubber materials.
European Patent 1029823 A2 also discloses the rubber materials as being selected from the group consisting of natural rubber, isoprene rubber, chloroprene rubber, styrene rubber, nitrile rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, butadiene rubber, styrene-butadiene rubber, butyl rubber, epichlorohydrin rubber, acrylic rubber, urethane rubber, fluoro rubber and silicone rubber. This European Patent also specifies the polar group of said first guest molecule and/or said main guest molecule is at least one selected from the group consisting of hydroxyl group, halogen group, carboxyl group, anhydrous carboxylic acid group, Thiokol group, epoxy group and amino group. The polar functional groups are present on the first or main guest molecules. However, this patent application does not require or suggest that the polar functional groups can be present on the “rubber material.”
European Patent 1029823 A2 suggests the method of producing a composite clay rubber material. It calls for the onium ion containing unsaturated groups and be crosslinked with the unsaturated groups of the guest molecules and also the rubber material. One embodiment of European Patent 1029823A2 calls for first incorporation of the clay with onium ion by contacting it with the first and second guest molecules. The process for incorporation or pre-dispersion of the clay in the guest molecules for preparing a clay-masterbatch required rather long mixing times for expanding or separating the clay layers and is considered herein somewhat industrially uneconomical. The masterbatch of the clay in the guest molecules was further kneaded with the rubber material to make the rubber-clay composite.
European Patent 1029823 A2 suggests the process for making a clay rubber material by blending with the rubber material. The first and second guest molecules were dissolved in a solvent when contacting the said rendered clay mineral. This additional step required long time for clay incorporation and furthermore, in such a process, all solvent was to be evaporated, which additionally requires considerable energy and extra care for handling solvents.
European Patent 1029823 A2 specifies the preferable main guest molecules as lauryl alcohol, stearyl aryl alcohol, oleyl alcohol, stearic acid, linolic acid, linolenic acid, stearyl chloride, or polyethylene, polypropylene or polyisoprene or polybutadiene with a polar group such as hydroxyl, carboxyl, epoxy or the like. This patent application mentions preparing a blend material of the composite clay material prepared with the guest molecule and synthetic resins such as polyethylene, polypropylene, polystyrene, polyisobutene, acrylic resin, polyurethane, and styrene-butadiene block copolymer. These resins have very limited use as rubber materials for use in tires and belts as many of these are not rubber-like materials. Resins like the styrene-butadiene block copolymers are not random copolymer rubbers that are generally used for specific performance achievement in tires & belts.
European Patent 1029823 A2 also specifies making the clay composite materials with two types of guest molecules, the first and the second. The first guest molecule had molecular length equal to or smaller than the onium ion and contained the polar group. The second guest molecule contained no polar group and had molecular weight exceed that of the onium ion. This process again required the use of two types of guest molecules for preparing the masterbatch. This patent application mentions the use of the second guest molecule with no polar groups as liquid polybutadiene, liquid polyisoprene, liquid butyl rubber or the like. Such liquid rubbers are known to plasticize the rubber materials and are known to generally improve processing of tire materials but at the same time, also increase the hysteresis or heat build-up or rolling resistance in a tire and are generally not used where low hysteresis and low rolling resistance are desired. This patent application also specifies making blend materials of the clay composite materials prepared with two types of guest molecules by blending with resins such as polyethylene, polypropylene, polybutylene, polyisoprene, polystyrene, acrylic resin, polyamide, polyester, or the like.
European Patent 1029823 A2 describes a composite clay rubber material obtained by kneading the composite clay materials prepared by blending the clay masterbatches of the guest molecules with the rubber like materials and crosslinking the guest molecule with rubber molecule. This European patent application also mentions that conventionally the rubber molecule cannot be uniformly dispersed in the clay mineral. European Patent 1029823 A2 has supposedly solved the problem of achieving a uniform dispersion of clay in a rubber material by masterbatching the clay mineral in the guest molecules and subsequently dispersing the masterbatch in a rubber material and crosslinking the guest molecules and rubber materials. Therefore, there is a need for obtaining the uniform dispersion of clay mineral in the rubber material without the need of pre-dispersion or masterbatching of the clay mineral in the guest molecules, firstly to eliminate the time consuming process of masterbatching, and secondly to eliminate the first and second guest molecules from the rubber materials, as they may deteriorate the properties due to plasticization or other undesirable effects in vulcanized articles of tire or belt rubber materials.
European Patent 1029823A2 does not teach that a light weight tire composition can be obtained. The said application does not teach that a low rolling resistance tire material can be developed. Furthermore, there is a need for a light-weight and low rolling resistance rubber material that can be prepared without the need for masterbatching of the clay in the guest molecules, for better production economies and better performance.